The Costa Rican forward left Pride Park in acrimonious circumstances after he was accused of being a "disruptive influence" towards the end of last season. But Wanchope insisted that he never asked to leave Derby, and that he was "hurt" by the way the club had dealt with the situation.
"I wasn't looking to move from Derby," Wanchope said, "but things changed and I am here now. It hurt me to be accused of being a disruptive influence - it is horrible. But I know what I did for that club, so I feel okay.
"I got on well with the fans there. When a player works hard and does things right he hopes he will get a good reception and now I hope that will happen for me at West Ham."
Wanchope, who has signed a four-year deal at Upton Park, scored 10 goals last season. He was watched by clubs on the Continent, but instead opted to sign for the West Ham manger, Harry Redknapp. "There was interest in me from Italy but I wanted to stay in the Premier League," Wanchope said. "I like the way West Ham play football and I am looking forward to being part of the team."
Redknapp expressed his delight at the deal. "I like people with ability and Paulo is a special player," he said. "He is a match-winner and I like to go into games with someone who can do things which are a little bit different.
"He is only 22, and he is a great athlete, who has pace. He has signed for four years and I think he will be a great asset."
Wanchope is awaiting his new work permit to come through but is expected to make his Hammers debut against Charlton in Keith Peacock's testimonial next Friday.
Wanchope's arrival has cast doubt on the future of Ian Wright. "I don't want him to go but if he says he wants to go somewhere he can have regular first-team football for his last year then I won't stand in his way," Redknapp said.
Redknapp is also hoping to re-sign Slaven Bilic, who was sold to Everton for pounds 4.5m, on a free transfer. "If I can get Slaven back for nothing it will be great business," he said.
The Liverpool defender Frode Kippe has broken his cheekbone in training. The Norwegian suffered the injury in an accidental clash of heads and is expected to be out for at least a month.
The Everton goalkeeper Thomas Myhre is hoping to available for selection by September. Myhre broke his ankle playing for Norway in May.